Nanostructured transparent conformal metal oxide coatings on different substrates have gained an increasing interest in many areas. Their applicability ranges from optics, electronics, solar energy conversion, and corrosion and abrasion protection to bioengineering.
Common methods for producing such coatings are dipping, spraying or spin coating by use of polymeric sols obtained via sol-gel technology. This well known technology is based on hydrolysis and poly-condensation of metal alkoxides. The chemistry involved in sol-gel process is based on inorganic polymerization (Yoldas, 1986; Kallala et al., 1992; Livage et al., 1988; Sanchez and Ribot, 1994). Hydrolysis and condensation reactions are both multiple-step processes, occurring sequentially and in parallel, and ultimately lead to the formation of oxopolymers. Non-silicate metal alkoxides such as those of transition metals, lanthanides, aluminium and tin are very sensitive to moisture (Livage et al., 1988; Sanchez and Ribot, 1994).
In order to obtain transparent sols, a control of hydrolysis and condensation is necessary. This control may be achieved through the use of inhibitors such as inorganic acids or complexing ligands like glycols, organic acids and β-diketones (Livage et al., 1988; Sanchez and Ribot, 1994). It is known that the simplest inhibitors for condensation reactions are protons (H+ions) commonly supplied by inorganic acids such as hydrochloric acid or nitric acid (Yoldas, 1986; Kallala et al., 1992; Livage et al., 1988; Sanchez and Ribot, 1994).
The combination of iodine, acetone and water leads to the formation of free H+ions according to the following reactions (Koura et al., 1995):
(1) CH3COCH3  CH3C(OH)CH2 
(2) CH3C(OH)CH2+I2 → CH3COCH2I+H++I−
The first reaction is a keto-enol equilibrium catalyzed by water and iodine, followed by the second reaction between enol-acetone and iodine giving H+ions.